The present invention relates to a nonvolatile semiconductor memory device. More particularly, it relates to techniques which are effective when utilized for, e. g., an electrically rewritable nonvolatile memory device of one-element/bit construction that has floating gate type nonvolatile memory elements.
A floating gate type nonvolatile memory device of one-element/bit construction, in which one bit (one memory cell) is constructed of a single nonvolatile memory element of the floating gate type and which is rewritable, is discussed in, for example, "ISSCC 88 Digest of Technical Papers", pp. 132-133. An erasing method for the floating gate type nonvolatile memory device is also discussed in the literature, and it consists in that, as in an EPROM (erasable and programmable read only memory), a high voltage is applied to a source line common to all bits, thereby to collectively erase all the bits. As the erasing high voltage, an external supply voltage is directly applied through a switch MOSFET (insulated-gate field effect transistor) or the like.